Boolean expressions
Groovy支持标准的条件运算符的布尔表达式：
1 | def a = true |
2 | def b = true |
3 | def c = false |
4 | assert a |
5 | assert a && b |
6 | assert a || c |
7 | assert !c |
此外，Groovy中有强制转换非布尔对象为布尔值的特殊规则。
集合
空集合会被强制转换为false：
1 | def numbers = [1,2,3] |
2 | assert numbers //true, as numbers in not empty |
3 | numbers = [] |
4 | assert !numbers //true, as numbers is now an empty collection |
迭代器和枚举
没有进一步元素的枚举和迭代器都会被强制转换为false：
1 | assert ![].iterator() // false because the Iterator is empty |
2 | assert [0].iterator() // true because the Iterator has a next element |
3 | def v = new Vector() |
4 | assert !v.elements() // false because the Enumeration is empty |
5 | v.add(new Object()) |
6 | assert v.elements() // true because the Enumeration has more elements |
Map
非空的map被强制转换为true：
1 | assert ['one':1] |
2 | assert ![:] |
Matchers
当匹配到正则表达式的模式的时候会强制转换为true:
1 | assert ('Hello World' =~ /World/) //true because matcher has at least one match |
Strings
非空的Strings, GStrings 和CharSequences 将被强制转换为true：
1 | <div> |
2 | <div> |
3 | <pre><code data-result="[object Object]">// Strings |
4 | assert 'This is true' |
5 | assert !'' |
6 | //GStrings |
7 | def s = '' |
8 | assert !("$s") |
9 | s = 'x' |
10 | assert ("$s") |
Numbers
非0的数值被强制转换为true，就如同perl一样。
1 | <div> |
2 | <div> |
3 | <pre><code data-result="[object Object]">assert !0 //yeah, 0s are false, like in Perl |
4 | assert 1 //this is also true for all other number types |
Object references
非null的对象引用被强制转换为true：
1 | assert new Object() |
2 | assert !null |
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本文转自被遗忘的博客园博客，原文链接：http://www.cnblogs.com/rollenholt/p/3349055.html，如需转载请自行联系原作者